This research will examine how "molecular" (small-scale) variables affect choice behavior. One major variable to be investigated will be delay of reinforcement, and its role in "self-control" choices (where a subject must choose between a small, immediate reinforcement and a larger but delayed reinforcer). Delay of reinforcement is also involved in subjects' preferences for variable as opposed to fixed reinforcemtnt schedules, and such preferences will also be investigated. Choice behavior will also be studied in situations where the alternatives include one certain reinforcer and one probabilistic reinforcer. The research will explore how such factors as level of motivation, the availability of alternative sources of reinforcement, and discriminative stimuli can affect performance in these choice situations. The subjects will be pigeons and rats performing in standard operant conditioning chambers, and an adjusting delay procedure developed by the PI will be used to measure preference. One major theoretical goal of the proposed research is to develop a mathematical theory which can incorporate all the variables mentioned above and predict how each will influence a subject's choice behavior. Many important everyday choices involve a conflict between an individual's short-term and long-term interests (e.g., the pleasures of smoking, drinking, or overeating versus future health). For this reason, it seems appropriate to submit this proposal, which is directed toward developing a better understanding of the effects of delayed and uncertain reinforcers, to NIMH.